Daniel C. Thompson, a 19-year-old football standout who dreamed of playing professionally or owning a computer consulting company, was slain last year during a robbery near a Metro station in Northeast Washington.

His assailants took nothing more than a cell phone and a pair of sneakers.

They used the phone once. They probably weren't able to wear Thompson's size 14 Nikes.

Nearly 18 months later, Thompson's killing remains a mystery, an example of the violence that has plagued the District during the past few decades. The police department has about 2,500 unsolved homicide cases out of some 4,800 slayings committed since 1990, according to department statistics. More than 4,100 homicides remain unsolved since 1968, the first year for which data are available.

Thompson's case remains open despite the best efforts of detectives who began investigating it in June 2003, police said. The lead detective believes the case might be connected to a spree of robberies. He has scoured robbery reports, tracked down robbery victims and even located people contacted over stolen cell phones, hoping to draw a link between the holdups and the killing.

But the work has yielded few clues, police said.

Detective James Broadbent, who has been investigating homicides for four years and is handling Thompson's case, said the killing is frustrating.

"This is a little tougher than most of them," said Broadbent, 37, who joined the force in 1989. "In most cases, you know who your suspect is and you try to find witnesses. In this case, I have neither."

Detectives believe that Thompson was the victim of two armed robbers who committed several holdups in the days before and months after the killing. The robbers specialized in taking cell phones, police said.

Just after 11 p.m. on June 15, Thompson was returning home after a visit to his girlfriend's apartment in the Mayfair complex in Northeast. He had just crossed a footbridge over Interstate 295 and turned onto a lighted walkway leading to the Minnesota Avenue Metro station when the two assailants approached and robbed him, police said.

One of the men shot Thompson, and the robbers fled.

Police learned about the shooting after a driver heading north on I-295 pulled into a gas station and used a pay phone to call authorities. He had seen three men on the walkway and a muzzle flash, he told operators before hanging up.

A woman who walked by Thompson thought he had passed out. She reported him to a Metro employee and left, Broadbent said.

Broadbent said he has been seeking the two witnesses ever since. He believes the motorist might even be able to identify the killers.

"Seeing somebody get shot is not something people see every day," Broadbent said. "That is something that is going to stick in your mind."

Besides scouring robbery reports and questioning victims, Broadbent and his partner, Detective Kenneth Arrington, have visited the neighborhood dozens of times, handing out fliers and talking to community groups.

But the detectives say they are no closer to solving the case than on that warm June night. They don't even know in which direction the assailants fled. And they have been unable to nail down more than a vague description of the killers, described as being in their late teens or early 20s. One is about 6 feet tall, and the other is about 5 feet 7 inches. One had cornrows.

As police have spent months trying to crack the case, Thompson's family has grieved.

"My life is empty without him," said Thompson's grandmother, Annie Alston, 77.

Thompson's mother, Doretha Thompson, keeps her son's funeral program, news clippings, notes from friends and other reminders in a plastic bag. She and her mother, Alston, essentially raised Thompson by themselves. It wasn't always easy, and his mother said she worked to keep Thompson on the right path.

Once, when he was in fifth grade, he left his two-floor rowhouse in Southeast and went to nearby D.C. General Hospital. He and some buddies climbed to the top of one of the buildings, and several tossed rocks at passersby.

When he got caught, he pleaded innocence to his mother, saying he hadn't thrown any rocks. But she didn't care, she said, and laid down the law.

After that, Thompson made a point of hanging out with better crowds and began to create his own identity. He became a Dallas Cowboys fan -- while living a few blocks from Robert F. Kennedy Memorial Stadium, the home of the Redskins. He refused to wear a Redskins jacket purchased as a gift by his mother.

"He was his own person," his mother said. "That's for sure."

He loved computers and helped family friends set up programs and operating systems. As a graduation gift, his grandmother bought him a $2,000 machine. He worked on it daily until his death, his mother said.

While he enjoyed computers, Thompson's true passion was football. At H.D. Woodson High School, he excelled as a 300-pound offensive lineman. In 2002, he helped lead Woodson to a city championship.

Thompson, who was 6 feet 3 inches tall and weighed more than 250 pounds at the time of his death, longed to play for powerhouse Louisiana State University. He never learned that his hopes had moved closer to reality.

Just hours after he was killed, his coach at Woodson was informed that Thompson had been accepted at Allegany College of Maryland, where he could hone his football skills and prepare to move on to a bigger program.

Thompson, a former standout football player at H.D. Woodson High School, was killed near the Minnesota Avenue Metro station.Detectives Kenneth Arrington, left, and James Broadbent have been unable to identify suspects in the fatal shooting of Daniel C. Thompson, 19, despite 18 months of searching records, interviewing robbery victims and meeting residents.Detectives Arrington and Broadbent hope to find a man who reported seeing a shooting near this walkway and a woman who saw Thompson's body.